在我要等待的方法上获取无法等待的空隙 [英] Getting a Cannot await void, on a method that I have want to await on

问题描述

我正在编写WPF应用程序.我们必须做到这一点，以便当用户隐藏/显示不同的列时，它将在一个视图的ReportViewer控件中反映出来.在测试中，我们发现将数据添加到ReportViewer的数据源需要很长时间.有时大约是几秒钟到一分钟.我认为对于用户来说太久了.所以我试图使用C#的异步并等待.但是，当我将await应用于进程hog的行，然后对其进行编译时，我从C#编译器收到一个错误:无法等待'void'".在这种情况下，我无法更改.NET框架返回的内容，即无效.那么我该如何处理这种情况呢?这是代码:

I'm on a team writing a WPF app. We have to make it so that when a user hides/shows different columns that it will reflect that in a ReportViewer control on one of the views. In testing we've found that it takes a long time to add the data to the ReportViewer's data sources; sometimes on the order of several seconds to possibly a minute. Too long I think for the users. So I'm trying to use C#'s async and await. However, when I applied await to the line that is the process hog and then compile it, I get an error from the C# compiler, "Cannot await 'void'". In this case, I cannot change what the .NET framework returns, its void. So how do I handle this situation? Here's the code:

private async Task GenerateReportAsync()
{
    DataSet ds = new DataSet();
    DataTable dt = new DataTable();
    dt.Clear();
    int iCols = 0;
    //Get the column names
    if (Columns.Count == 0)     //Make sure it isn't populated twice
    {
        foreach (DataGridColumn col in dataGrid.Columns)
        {
            if (col.Visibility == Visibility.Visible)
            {
                Columns.Add(col.Header.ToString());     //Get the column heading
                iCols++;
            }
        }
    }
    //Create a DataTable from the rows
    var itemsSource = dataGrid.ItemsSource as IEnumerable<Grievance>;
    if (this.rptViewer != null)
    {
        rptViewer.Reset();
    }
    rptViewer.LocalReport.DataSources.Clear();
    if (m_rdl != null)
    {
        m_rdl.Dispose();
    }
    Columns = GetFieldOrder();
    m_rdl = CoreUtils.GenerateRdl(Columns, Columns);
    rptViewer.LocalReport.LoadReportDefinition(m_rdl);
    //the next line is what takes a long time
    await rptViewer.LocalReport.DataSources.Add(new ReportDataSource("MyData", CoreUtils.ToDataTable(itemsSource)));
    rptViewer.RefreshReport();
}

推荐答案

对于本质上是同步的方法，您需要将它们包装在自己的Task中，以便等待.在您的情况下，我只使用Task.Run:

For methods that are inherently synchronous, you need to wrap them in your own Task so you can await it. In your case, I would just use Task.Run:

await Task.Run(() => 
{
   rptViewer.LocalReport.DataSources.Add(new ReportDataSource("MyData", CoreUtils.ToDataTable(itemsSource)));
});

还有其他生成任务的方法，但这可能是最简单的方法.如果此操作更新了UI组件，则可能会引发异常，因为这些操作必须在UI线程上进行.在这种情况下，请尝试使与UI相关的部分远离长时间运行的部分，而仅将较长的部分包装在Task中.

There are other ways to generate a task, but this one is probably the easiest. If this updates a UI component, it will likely throw an exception because those operations must occur on the UI thread. In this case, try to get the UI related piece away from the long-running part and only wrap the long part in the Task.

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